The traditional electric bulbs consume high amount of electric energy and no longer meet nowadays requirement for energy saving. The illumination technology employing light-emitting diodes (LED) has been developed to replace the traditional electric bulbs with LED lamps for the purpose of energy saving. While the currently available LED lamps have high power to increase illumination thereof, they also produce high amount of heat during the operation thereof, and the produced heat is not easily dissipated. Moreover, the currently available LED lamps are not easy to assemble, and are not adjustable in the number of LEDs thereof for providing desired illuminance (lumen). Due to these factors, the current LED lamps always require high production cost. It is therefore tried by the inventor to develop an LED lamp that is easy to assemble and may have adjustable number of LEDs to meet different requirements for illuminance.